This disclosure relates to the field of drilling extended reach lateral wellbores in formations below the bottom of a body of water. More specifically, the invention relates to drilling such wellbores where a sub-bottom depth of a target formation is too shallow for conventional directional drilling techniques to orient the wellbore trajectory laterally in the target formation.
Lateral wellbores are drilled through certain subsurface formations for the purpose of exposing a relatively large area of such formations to a well for extracting fluid therefrom, while at the same time reducing the number of wellbores needed to obtain a certain amount of produced fluid from the formation and reducing the surface area needed to drill wellbores to such subsurface formations.
Lateral wellbore drilling apparatus known in the art include, for example and without limitation, conventional drilling using segmented drill pipe supported by a drilling unit or “rig”, coiled tubing having a drilling motor at an end thereof and various forms of directional drilling apparatus including rotary steerable directional drilling systems and so called “steerable” drilling motors. In drilling such lateral wellbores, a substantially vertical “pilot” wellbore may be drilled at a selected geodetic position proximate the formation of interest, and any known directional drilling method and/or apparatus may be used to change the trajectory of the wellbore to approximately the geologic structural direction of the formation. When the wellbore trajectory is so adjusted, drilling along the geologic structural direction of the formation may continue either for a selected lateral distance from the pilot wellbore or until the functional limit of the drilling apparatus and/or method is reached. It is known in the art to drill multiple lateral wellbores from a single pilot wellbore to reduce the number of and the cost of the pilot wellbores and to reduce the surface area needed for pilot wellbores so as to reduce environmental impact of wellbore drilling on the surface.
Some formations requiring lateral wellbores are at relatively shallow depth below the ground surface or the bottom of a body of water. In such cases using conventional directional drilling techniques may be inadequate to drill a lateral wellbore because of the relatively limited depth range through which the wellbore trajectory may be turned from vertical to the dip (horizontal or nearly so) of the formation of interest.